A Light Emitting Diode (LED) manufacturing plant based in Penang, Malaysia produces 800 million units annually. Exported globally, the manufactured components are mainly used in LED television sets and lighting for automobiles. A number of production steps, such as the oven process and the circuit and integrity tests, are carried out on the manufacturing line. In order to verify that all finished components have gone through each stage and have passed the required tests, the manufacturer chose a reliable traceability system featuring DataMan? barcode readers that read laser-marked 2-D codes on each LED strip at every production stage.

Sources of Challenges

The materials that are used for LED production come from various suppliers and countries. Each supplier uses a different grade of laser marker to imprint its 2-D codes, resulting in variable print quality. The types of ceramics used may also be different, further compounding the problem. Due to the miniature sizes of the components, each 2-D code typically measures less than two millimeters. In addition, LEDs are put through an oven process where electrical component leads are joined to the board via individual pad connections located on the board surface.

The heat applied (approximately 300?C) to dry the soldered connections sometimes causes distortion to the codes. The manufacturer's existing barcode scanning system could not deliver a 100 per cent successful read -rate due to these challenges.

Part of the problem can be attributed to the fact that some of the scanners initially deployed were handheld readers, which were not designed for high-speed barcode reading on fast-moving production lines. Whenever a 'no read' occurred, operators had to manually enter information, which is disruptive to the entire manufacturing process. Furthermore, with the ramping up of production volume over time, the need for a reliable solution that could handle high-speed volumes started to become increasingly apparent.

Solution

The manufacturer's initial deployment of DataMan barcode readers achieved a success read rate of 100 per cent. After the initial deployment, an additional 15 DataMan barcode readers have been installed so the LED manufacturer could achieve full component traceability.

DataMan barcode readers enable manufacturers to achieve full production traceability so if component misses a test or a human error were to occur, the process could reject a part or display an error when the barcode was read at the next process step. From a quality assurance point of view, having such a traceability system in place ensures that every component that exits the line has already passed through all the required testing stages.

Reading Technology

Some of the key features of the DataMan 300 barcode reader that was chosen for this application are its high resolution (1.3 megapixel) and flexible lighting options. The environment for this application required high-resolution images for success, since barcodes were small.

In addition, blue lighting was used for the application to ensure optimal read rates. The DataMan barcode reader enables users to control light intensity and has a bank of lighting that can be configured to be turned on bi-directionally, unidirectional or from all directions.

After fine-tuning, the resulting image was of a better quality and had the strong contrast that was needed. This improved the overall performance of the reading operation from 90 per cent to 100 per cent.

Another requirement was that the reader had to be deployed at a 'safe' distance from the items that it was scanning. The main concern was if the reader were placed too close, static electricity from the reader could damage the electronic circuits of the LED. A second consideration was that the operator might accidentally knock against the reader, while trying to manually remove an LED from the production line. Given these two factors, the manufacturer located the reader about eight centimeters away from the items that are being scanned. The high resolutions offered by the DataMan readers facilitate this option, as they are able to produce magnified images with the necessary clarity, even at this distance.

Optimising Capabilities

In order to customize the solution to each application on the production line, the implementation team had to experiment with different levels of magnification. This was possible because the lens on the reader is adjustable. The software code needed to be 'trained' to read the small 2D codes. This allowed the system to memorize the properties of the codes, such as module and pixel sizes, effectively optimising read-rate performance.

Another issue that had to be addressed is how the reader is being triggered for each individual process. There was also a need to determine how data from the reader is sent to the corresponding machine or PC.

Much effort had to be invested in testing out different configurations to achieve optimum performance. Light intensity, exposure values and lens distance were just some of the elements that had to be considered. Samples of the product items from various suppliers also had to be extensively studied to understand how they affected read capabilities.

(Contact: Sunil Vaggu, Cognex Sensors India Pvt Ltd. Mobile: 098814-66003. Email: vaggu.sunil@cognex.com)